High quality sound systems require amplifiers which produce good sound quality. Sound quality is not something that may easily be measured and an amplifier which may have good physical characteristics such as a wide frequency response at both low and high frequencies, low phase shift and low distortion, may not necessarily produce good quality sound. The reason for this appears to be due to errors or distortions which are not obvious from studying the amplifier's physical characteristics. These distortions may be reduced by applying overall negative feedback.
For audio applications, it is believed that amplifiers without feedback may have desirable characteristics that are good for sound. However, amplifiers without feedback usually do not have good measurement characteristics, such as total harmonic distortion (THD) measurements, when compared to amplifiers that utilise feedback.
There is therefore a need for amplifiers which have improved measurement characteristics and therefore improved performance, irrespective of whether or not feedback is applied.